This paper reports on an intervention study which investigated the effect of teaching English phonotactics upon Arabic speakers' lexical segmentation of running speech in English. The study involved a native English-speaking group (N = 12), a non-native control group (N = 20); and a non-native experimental group (N = 20). Each group was pre-tested using a Word Spotting Task which investigated the extent to which illegal consonant clusters in English and Arabic supported the lexical segmentation of English. The non-native groups were post-tested with the same task after 8 weeks, during which the experimental group was given a treatment consisting of explicit teaching of relevant English phonotactic constraints. Post-test results showed significant gains in the segmentation ability of the experimental group. (Contains 1 figure and 1 table.)